This invention relates to emergency medical devices and methods and the resuscitation of cardiac arrest patients.
Cardiopulmonary resuscitation (CPR) is a well known and valuable method of first aid. CPR is used to resuscitate people who have suffered from cardiac arrest after heart attack, electric shock, chest injury and many other causes. During cardiac arrest, the heart stops pumping blood, and a person suffering cardiac arrest will soon suffer brain damage from lack of blood supply to the brain. Thus, CPR requires repetitive chest compression to squeeze the heart and the thoracic cavity to pump blood through the body. Very often, the patient is not breathing, and mouth to mouth artificial respiration or a bag valve mask is used to supply air to the lungs while the chest compression pumps blood through the body.
It has been widely noted that CPR and chest compression can save cardiac arrest patients, especially when applied immediately after cardiac arrest. Chest compression requires that the person providing chest compression repetitively push down on the sternum of the patient at 80 to 100 compressions per minute. CPR and closed chest compression can be used anywhere, wherever the cardiac arrest patient is stricken. In the field, away from the hospital, it may be accomplished by ill-trained bystanders or highly trained paramedics and ambulance personnel.
When a first aid provider performs chest compression effectively, blood flow in the body is typically about 25 to 30% of normal blood flow. This is enough blood flow to prevent brain damage. However, when chest compression is required for long periods of time, it is difficult if not impossible to maintain adequate compression of the heart and rib cage. Even experienced paramedics cannot maintain adequate chest compression for more than a few minutes. Hightower, et al., Decay In Quality Of Chest Compressions Over Time, 26 Ann. Emerg. Med. 300 (September 1995). Thus, long periods of CPR, when required, are not often successful at sustaining or reviving the patient. At the same time, it appears that, if chest compression could be adequately maintained, cardiac arrest victims could be sustained for extended periods of time. Occasional reports of extended CPR efforts (45 to 90 minutes) have been reported, with the victims eventually being saved by coronary bypass surgery. See Tovar, et al., Successful Myocardial Revascularization and Neurologic Recovery, 22 Texas Heart J. 271 (1995).
In efforts to provide better blood flow and increase the effectiveness of bystander resuscitation efforts, modifications of the basic CPR procedure have been proposed and used. Of primary concern in relation to the devices and methods set forth below are the various mechanical devices proposed for use in main operative activity of CPR, namely repetitive compression of the thoracic cavity.
The device shown in Barkolow, Cardiopulmonary Resuscitator Massager Pad, U.S. Pat. No. 4,570,615 (Feb. 18, 1986), the commercially available Thumper device, and other such devices, provide continuous automatic closed chest compression. Barkolow and others provide a piston which is placed over the chest cavity and supported by an arrangement of beams. The piston is placed over the sternum of a patient and set to repeatedly push downward on the chest under pneumatic power. The patient must first be installed into the device, and the height and stroke length of the piston must be adjusted for the patient before use, leading to delay in chest compression. Other analogous devices provide for hand operated piston action on the sternum. Everette, External Cardiac Compression Device, U.S. Pat. No. 5,257,619 (Nov. 2, 1993), for example, provides a simple chest pad mounted on a pivoting arm supported over a patient, which can be used to compress the chest by pushing down on the pivoting arm. These devices are not clinically more successful than manual chest compression. See Taylor, et al., External Cardiac Compression, A Randomized Comparison of Mechanical and Manual Techniques, 240 JAMA 644 (August 1978).
Other devices for mechanical compression of the chest provide a compressing piston which is secured in place over the sternum via vests or straps around the chest. Woudenberg, Cardiopulmonary Resuscitator, U.S. Pat. No. 4,664,098 (May 12, 1987) shows such a device which is powered with an air cylinder. Waide, et al., External Cardiac Massage Device, U.S. Pat. No. 5,399,148 (Mar. 21, 1995) shows another such device which is manually operated. In another variation of such devices, a vest or belt designed for placement around the chest is provided with pneumatic bladders which are filled to exert compressive forces on the chest. Scarberry, Apparatus for Application of Pressure to a Human Body, U.S. Pat. No. 5,222,478 (Jun. 29, 1993), and Halperin, Cardiopulmonary Resuscitation and Assisted Circulation System, U.S. Pat. No. 4,928,674 (May 29, 1990), show examples of such devices. Lach, et al., Resuscitation Method and Apparatus, U.S. Pat. No. 4,770,164 (Sep. 13, 1988), proposed compression of the chest with wide band and chocks on either side of the back, applying a side-to-side clasping action on the chest to compress the chest.
Several operating parameters are required for a successful resuscitation device. Chest compression must be accomplished vigorously if it is to be effective because very little of the effort exerted in chest compression actually compresses the heart and large arteries of the thorax and most of the effort goes into deforming the chest and rib cage. The force needed to provide effective chest compression, however, creates risk of other injuries. It is well known that placement of the hands over the sternum is required to avoid puncture of the heart during CPR. See Jones and Fletter, Complications After Cardiopulmonary Resuscitation, 12 Am. J. Emerg. Med. 687 (November 1994), which indicates that lacerations of the heart, coronary arteries, aortic aneurysm and rupture, fractured ribs, lung herniation, stomach and liver lacerations have been caused by CPR. Thus the risk of injury attendant to chest compression is high, and clearly may reduce the chances of survival of the patient vis-à-vis a resuscitation technique that could avoid those injuries. Further, chest compression will be completely ineffective for very large or obese cardiac arrest patients because the chest cannot be compressed enough to cause blood flow. Additionally, chest compression via pneumatic devices is hampered in its application to females due to the lack of provision for protecting the breasts from injury and applying compressive force to deformation of the thoracic cavity rather than the breasts.
CPR and chest compression should be initiated as quickly as possible after cardiac arrest to maximize its effectiveness and avoid neurologic damage due to lack of blood flow to the brain. Hypoxia sets in about two minutes after cardiac arrest, and brain damage is likely after about four minutes without blood flow to the brain. Further, the severity of neurologic defect increases rapidly with time. A delay of two or three minutes significantly decreases the chance of survival and increases the probability and severity of brain damage. However, CPR and ACLS are unlikely to be provided within this time frame. Response to cardiac arrest is generally considered to occur in four phases, including action by Bystander CPR, Basic Life Support, Advanced Cardiac Life Support, and the Emergency Room. Bystander CPR occurs, if at all, within the first few minutes after cardiac arrest. Basic Life Support is provided by First Responders who arrive on scene about 4 to 6 minutes after being dispatched to the scene. First responders include ambulance personnel, emergency medical technicians, firemen and police. They are generally capable of providing CPR but cannot provide drugs or intravascular access, defibrillation or intubation. Advanced Life Support is provided by paramedics or nurse practitioners who generally follow the first responders and arrive about 8 to 15 minutes after dispatch. ALS is provided by paramedics, nurse practitioners or emergency medical doctors who are generally capable of providing CPR, and drug therapy, including intravenous drug delivery, defibrillation and intubation. The ALS providers may work with a patient for twenty to thirty minutes on scene before transporting the patient to a nearby hospital. Though defibrillation and drug therapy are often successful in reviving and sustaining the patient, CPR is often ineffective even when performed by well trained first responders and ACLS personnel because chest compression becomes ineffective as the providers become fatigued. Thus, the initiation of CPR before arrival of first responders is critical to successful life support. Moreover, the assistance of a mechanical chest compression device during the Basic Life Support and Advanced Life Support stages is needed to maintain the effectiveness of CPR.
The devices described below provide for circumferential chest compression using a device which is compact, portable or transportable, self-powered with a small power source, and easy to use by bystanders with little or no training. Additional features may also be provided in the device to take advantage of the power source and the structural support board contemplated for a commercial embodiment of the device.
The device includes a broad belt which wraps around the chest and is buckled in the front of the cardiac arrest patient. The belt is repeatedly tightened around the chest to cause the chest compression necessary for CPR. The buckles and/or front portion of the belt are anatomically accommodating for the female breast, or for the obese person, so that the device is effective for women as well as men. The buckle may include an interlock which must be activated by proper attachment before the device will activate, thus preventing futile belt cycles. The operating mechanism for repeatedly tightening the belt is provided in a support board or in a small box locatable at the patient""s side, and comprises a rolling mechanism which takes up the intermediate length of the belt to cause constriction around the chest. The roller is powered by a small electric motor, and the motor is powered by batteries and/or standard electrical power supplies such as 120V household electrical sockets or 12V DC automobile power sockets (car cigarette lighter sockets). The belt is contained in a cartridge which is easily attached and detached from the motor box. The cartridge itself may be folded for compactness. The motor is connected to the belt through a transmission that includes a cam brake and a clutch, and is provided with a controller which operates the motor, clutch and cam brake in several modes. One such mode provides for limiting belt travel according to a high compression threshold, and limiting belt travel to a low compression threshold. Another such mode includes holding the belt taut against relaxation after tightening the belt, and thereafter releasing the belt. Respiration pauses, during which no compression takes place to permit CPR respiration, can be included in the several modes. In other embodiments, the motor is connected to the belt through a transmission that includes a non-reversing coupling, permitting simplified operation of the system, and brakes are connected to the system through take-offs from the drive train. Thus, numerous inventions are incorporated into the portable resuscitation device described below.
The portable resuscitation device may incorporate a number of features and accessories that aid in the administration of CPR and other therapy. Bystanders may be unable to confidently determine if chest compression is needed, or when it should be stopped. Accordingly, the device may be combined with an interlock system including a heart monitor or EKG which diagnoses the condition of the patient, and circuitry or a computer which initiates, permits or forbids belt operation accordingly. The power supply provided for belt constriction may also be used to provide power for defibrillation (an appropriate treatment for many cardiac arrests). Again, bystanders will most likely not be capable of determining when defibrillation is appropriate, and the defibrillation portion of the device may be provided with an interlock system including the heart monitor or EKG which diagnoses the condition of the patient and circuitry which initiates, permits, or forbids defibrillation. Expert systems implemented through the circuitry or computer modules can accomplish these functions.
Automatic, computer driven therapy of this nature may provide early and appropriate life saving response to many cardiac arrest patients who would otherwise die. However, some situations in which the device might be used call for expert supervision of the CPR process by emergency medical technicians, emergency room doctors, or cardiologists. To this end, the expert systems mentioned above may be replaced with the expert diagnosis and decision-making of medical personnel through a telemetry system housed within the support board of the device. The support board can include a telemetry system which automatically dials medical personnel in a nearby hospital, emergency medical crew, ambulance, or even a central diagnostic and control facility. Interlocks, limit switches and other typical sensors can be used to sense the proper position and closure of the belt about the chest of the patient. Heart monitors and EKG electrodes can sense the heart rate and EKG of the victim. Using communication equipment within the device, this information can be communicated from the device to medical personnel remote from the victim. Through the same system, the medical personnel can communicate with the device to initiate, permit or prohibit belt constriction or defibrillation, as dictated by preferred medical procedures. Communication can be established through normal telephone lines and a cordless telephone, or through a cellular telephone system, paging system, internet or any other communications system. The device can be programmed with location information, or provided with GPS capabilities to determine the location of the device, and this information can be automatically transmitted to an emergency response system such as the 911 system when the system is placed in use.